If you haven't trammed an antenna before, also be aware that unless the tram
line is very taught there is a lot of sag in the line as the antenna reaches
the top of the tower. With only 18 inches of clearance you'll have to keep
this in mind when you rig the tram line. Good luck.
73, Bob - W3YY
[mailto:email@example.com] On Behalf Of Al, N6TA
Sent: Sunday, November 23, 2008 4:54 AM
Subject: [TowerTalk] Tramming help sought
I won't bore the readers with the usual retread questions. Already did the
reading etc. and lowered the old beam a month ago. This is one on how to
rig the haul line to pull up the 110 lb SteppIr yagi.
The tram line is to be rigged about 3 feet above the top on the Rohn 45
tower which has a flat top plate. The boom will be mounted right above the
top plate. The tram line is continuous in that it goes thru a pulley and
down to a 'back stay point'. Trying to allow the tram line some ability to
move but direct most of the force down the mast to the rotor.
The beam will be hung from a sling that connects a pulley to the tram
line. The boom will hang about 18 inches below the tram line. A
tiller/torque arm will be attached 'behind' the boom, keeping the boom from
rotating in two axes.
The haul line is half inch polyester double braid and will be tied to the
boom close to the CG point. The bracket that holds the tram line above the
tower top has a place for a pulley to be mounted for the haul line, probably
attached with a snap link or shackle. The question I have is how to rig the
haul line's pulley such that I can pull straight down and not have
interference with the tower's top plate. The bracket for the pulley is
about 3 inches out from the mast and the tower needs about 9 inches
clearance from the mast to go straight down without rubbing on the edge of
the top plate. I fear way too much friction if I allow this. I lowered the
prior beam this way and used the friction to advantage but do not want such
issues when pulling up the new beam.
If I rig the haul line pulley ( a CMI 2.375 inch 95% eff. rescue type) such
that it is hanging out far enough to clear the top plate, I end up pulling
sideways on the mast.
There must be a standard practice here but I have not yet read any postings
about this detail. I usually just 'go for it' and keep the fingers
crossed. I have way too many PhDs in the School of Hard Knocks and prefer
to not get another....
If I can pull the beam up as far as it can get, to the haul line pulley, I
plan to relax the tram line and let it settle the boom down where it will
rest on the top plate until I can use other means to raise it the 6 inches
to the boom to mast plate.
Willing to call to talk about it.
Tnx in advance.
Yeah, I'm missing the CW test due to delay in getting this up.
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